Emulsions of asphalt, bitumen, and coal tar have a wide number of applications, including but not limited to the production of aggregate pavement. One of the problems encountered with asphalt emulsions is the length of time it takes for the emulsion to start to set and the time for the emulsion to dry. This is extremely expensive when traffic must be kept off a lane of a highway for a lengthy period of time. The properties of asphalt, bitumen, coal tar or a mixture thereof may be improved by the incorporation of a polymer. This improves adhesion, ductility, tensile strength, and cold temperature properties of the asphalt, bitumen or coal tar. This may be done by melting the asphalt and adding the polymer. This process is energy intensive. The addition of polymer to asphalt, bitumen, coal tar or a mixture thereof may be accomplished by mixing emulsions of such material with a latex of the polymer. While this process is less energy intensive, it further accentuates the delay in setting times and drying times of asphalt emulsions.
One approach to enhance the drying time of asphalt emulsions has been to include a silicofluoride gelling agent into the system. Examples of this approach include CA 96: 163961k of E.P. 45,619 published Feb. 10, 1982 in the name of the British Petroleum Co. Ltd.; CA 83: 196173g of Belgium Patent 821,210 published Feb. 17, 1975 in the name of Kamenouhelve Poly Oborove Rzeditelstvi; and CA 81:171549n of German Offen. 2,363,085 published July 4, 1974 in the name of Rambelli Giacinto. Silicofluorides are time dependent gelling agents. Thus, the silicofluoride is mixed with the emulsion shortly before the emulsion is to set. This necessitates a two component application system or use of the system immediately after adding the gelling agent. The silicofluorides are used as gelling agents with anionic emulsions.
One approach is to add one or more thickening agents to asphalt emulsions. This approach is taught by Duzak et al. (Hercules Inc.) U.S. Pat. No. 4,492,781 which discloses a composition of an emulsion of asphalt/rubber/acrylic copolymer (100-10:0-90:0-70), a water soluble polymer, reinforcing component, aggregate, a curing and thickening agent and a rosin ester. The acrylic polymer disclosed in the Hercules patent is a copolymer of ethylene and acrylic acid. The water soluble polymer described as RETEN is an acrylamide copolymer. Neither of these polymer types is the poly C.sub.3-4 ethylenically unsaturated carboxylic acid required in the present invention. Additionally, such polymer types do not improve the setting or drying time of emulsions of asphalt, bitumen or coal tar which have been modified with an aqueous emulsion of a polymer.
None of the prior art teaches that a cationic emulsion of asphalt, bitumen, coal tar, or a mixture thereof which has been modified with an aqueous emulsion of a polymer may in admixture with aggregate be set and dried at a faster rate by including relatively minor amounts of low molecular weight polymers of acrylic or methacrylic acid.
U.S. Pat. No. 3,493,408 issued Feb. 3, 1970 discloses clay dispersed bitumen emulsions stabilized with salts of oxalic acid. The present invention is not intended to be used with such emulsions as they are anionic.
As used in this specification the term set means the point at which aggregate in contact with an aqueous emulsion of bitumen, asphalt, tar or a mixture thereof is first resistant to movement. Setting time means the time it takes from initial contact with aggregate for an emulsion of asphalt, bitumen, tar or a mixture thereof to set.